Direct current lightning arrester with automatic arc quenching means



Nov. 24, 1970 s. R. SMITH. JR

DIRECT CURRENT LIGHTNING ARRESTER WITH AUTOMATIC ARC QUENCHING MEANS 2 Sheets-Sheet 1 Filed July 18, 1968 Nov. 24, 1970' s. R. SMITH. JR 3,

, DIRECT CURRENT LIGHTNING ARRESTER WITH AUTOMATIC ARC QUENCHING MEANS Filed July 18, 1968 2 Sheets-Sheet 2 vu/e l3 PEI/570R United States Patent C) 3,543,097 DIRECT CURRENT LIGHTNING ARRESTER WITH AUTOMATIC ARC QUENCHING MEANS Sidney R. Smith, Jr., Myrtle Beach, S.C., assignor to General Electric Company, a corporation of New York Filed July 18, 1968, Ser. No. 745,933 Int. Cl. H02h 1/00 US. Cl. 317-68 18 Claims ABSTRACT OF THE DISCLOSURE A lighting arrester having a spark gap assembly with a pair of .main spark gap electrodes and with one or more auxiliary electrodes disposed in proximity to the main electrodes and adapted to be electrically contacted by an are formed across the spark gap. The auxiliary electrodes are connected to a source of voltage that introduces an electric discharge into the main spark gap are when the arc moves into contact with these electrodes. This electric discharge facilitates extinction of the are, as a direct function of arc voltage, independent of power-follow current voltage.

My invention relates to lightning arrester spark gaps of the current limiting type and, more particularly, to means for introducing an electric discharge into an arc formed between the spark gap electrodes of a direct current lightning arrester to facilitate extinction of the are formed between these electrodes.

As is well known, lightning arresters are utilized with electric systems to perform two basic functions. First, lightning arresters are operatively connected to a system at predetermined points to protect it from damage due to overvoltage surges which may be initiated by system transient voltages, such as those due to normal switching functions, or which may be initiated by lightning striking the system. Lightning arresters afford this primary function by discharging such surge voltages to ground so that no component of the protected system is subjected to an overvoltage that would damage it or other system components or insulation. The second basic function of lightning arresters is to reseal the surge voltage discharge path to ground following the discharge cycle of the arrester.

To improve the capability of a. lightning arrester to reseal following a discharge cycle, it is known in the prior art to provide current limiting spark gaps in series with the arresters discharge circuit. Such spark gaps rapidly increase are voltage following sparkover of the arrester, which completes a discharge circuit through the arrester to ground. This rapid increase in arc voltage is accomplished by lengthening and cooling the are formed between the primary spark gaps of the lightning arrester. By thus lengthening the arcs in the arresters discharge circuit, the arc resistance is sharply increased and therefore develops a greater voltage drop across the respective spark gaps of the arrester. Of course, such an introduction of increased series resistance simultaneously limits the amount of current flowing through the arrester. This operation of the current limiting spark gaps, combined with the action of series connected valve resistors utilized in conventional lightning arresters, serves to facilitate rapid extinction of an arc and reseal of the arresters following a transient overvoltage surge from a protected alternating current system. Essentially, the arrester is resealed by the introduction of high series resistance into the arrester discharge circuit by these means, because the resistance effectively prevents an are from restriking when the alternating current power-follow current is extinguished by cycling through zero voltage.

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Lightning arresters intended for use in protecting direct current electric systems must also provide some means for extinguishing power-follow current rapidly so that they can be resealed to insulate the system from ground following the discharge of a transient overvoltage surge. Of course, the power-follow current from such systems does not periodically cycle through zero voltage, but rather tends to stabilize at a level equal to the D-C line voltage of the system. Therefore, rescaling means in direct current arresters must be effective to interrupt powerfollow current which is at a continuous voltage level approaching the normal line voltage of the protected system.

Due to the nature of lighting arresters and the functions that they perform, it is desirable to provide such are extinction, or rescaling, means in a rugged form which will operate automatically and reliably without requiring frequent maintenance or inspection. Therefore, if possible it is desirable to provide mechanically and electrically simple means for performing this function. In addition, it is advantageous to provide lightning arresters with an accurate, and precisely predetermined, sparkover voltage level and ratio of reseal voltage to sparkover voltage. When the sparkover and reseal voltages of lightning arresters can be accurately predetermined, it is possible to improve the design parameters of protected systems so that optimum performance of the lightning arresters utilized with the system can be achieved. In the past, it has been found desirable to provide means for adjusting the ratio of sparkover voltage to reseal voltage of A-C lightning arrester and it is one object of my invention to provide a direct current lightning arrester spark gap assembly having means for adjusting this ratio.

A further object of my invention is to provide a spark gap assembly having means for automatically facilitating the extinction of an are formed therein at a precisely predetermined arc voltage.

Still another object of my invention is to provide a spark gap assembly having improved means for accurately adjusting the ratio of sparkover voltage to reseal voltage for the assembly.

Another object of my invention is to provide a direct current lightning arrester having a current limiting spark gap assembly with improved electrodynamic arc lengthening means.

Briefly stated, in one embodiment of my invention a direct current lightning arrester is provided with a spark gap assembly having a pair of spaced-apart primary electrodes disposed in an arcing chamber that is adapted to receive and cool an are stretched between the primary electrodes. Pursuant to my invention, one or more auxiliary electrodes are positioned in the arcing chamber a predetermined distance from the primary electrodes in a manner such that an arc stretched into the arcing chamber will electrically contact the auxiliary electrodes when the arc voltage attains a predetermined level. An auxiliary arcing chamber is provided to optimize the arc-extinguishing function of the invention.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a side elevation, partly in cross section, of a direct current lightning arrester embodying a preferred form of the invention.

FIGURE 2 is a schematic diagram of the electric circuitry of the lightning arrester depicted in FIGURE 1.

FIGURE 3 is a cut-away plan view of the spark gap assembly shown in FIGURE 1 of the drawing taken along plane 3-3 of FIGURE 1, in combination with a circuit diagram of a portion of the preferred embodiment of my invention.

FIG. 4 is a cross sectional, side elevation view of the preferred form of spark gap assembly shown in FIG. 3 taken along the plane 4-4 of FIG. 3.

FIG. is a side elevation view, partly in cross section, of a second embodiment of a spark gap assembly constructed according to the teaching of the invention.

FIG. 6 is a schematic plan view and circuit diagram of still another embodiment of a spark gap assembly arcing chamber constructed pursuant to the teaching of my invention, and shown with respect to a protected electric system.

Referring now to FIG. 1 of the drawing, there is shown a lightning arrester 1 having a tubular insulating housing 2 provided with conductive end caps 3 and 4 which are sealed, respectively, to the housing 1 by a suitable cement or resin compound 5. Moisture is prevented from entering the interior of the housing 2 by the metal plate 6 which is pressed into sealing engagement with an annular resilient washer 7, that is positioned in a preformed circular groove 8 around the upper end surface of the housing 2. In a similar manner, the lower end of the housing 2 is sealed by a rupturable, pressure-responsive diaphragm 9 that is compressed against an annular sealing Washer 10 to deform it into a positioning groove 11 in the bottom end of the housing 2. A gas venting passageway 12 affords communication from the interior of the housing 2 to the atmosphere through the end cap 4 for gases that may be generated by failure of the arrester, resulting in the rupture of the diaphragm 9, as is well known in the lightning arrester art.

Mounted within the lightning arrester housing 2 is a block of nonlinear valve resistance material 13, which rests on the rupturable diaphragm 9, and supports an end terminal plate 14 of a spark gap assembly 15 on its upper surface. The spark gap assembly 15 has a second end terminal plate 16 mounted on its uppermost surface. In order to retain the valve resistor 13 and the spark gap assembly 15 in electrically conductive relation, a compressed coil spring 17, having a shunting strap 18 extending between its opposite ends, is compressed between the terminal plate 16 on the spark gap assembly 15 and the end terminal plate 6 of the lightning arrester 1. The specific electric circuitry and electrode structure utilized in the spark gap assembly 15, which forms a significant part of my invention, will be described in greater detail below. At this point, it is only necessary to understand that the spark gap assembly 15 includes a plurality of porous insulating discs A, B, C and D, which are stacked in matched pairs on opposite sides of an electrically conductive coil 19, which develops magnetic flux to facilitate arc movement within the spark gap assembly in a manner well known in the lightning arrester field. It should be appreciated that the component parts of the lightning arrester 1 that have been described thus far may be formed of any suitable material or combinations of material and arranged in various conventional configurations. Therefore, I do not intend that the scope of my invention be limited to the particular materials or configurations described thus far.

A fuller understanding of the electrical function and structural arrangement of the operating components of lightning arrester 1 may be obtained by referring to FIG. 2 wherein these operating components are diagrammatically illustrated. Thus it will be noted, that between the end cap terminals 3 and 4 of the lightning arrester 1, a series circuit is formed containing the nonlinear resistance valve 13 and two main series connected spark gaps A'B' and C'-D'. Electrically connected in series between these main spark gaps is the arc-moving coil 19 and an overvoltage protective gap 20 for coil 19. In normal use, the circuit thus described would be electrically connected by a suitable conductor 21 to a conductive member 22 of an electric system which is to be protected by the arrester 1. Also, the terminal plate 4 of the arrester would normally be grounded, as shown in FIG. 2. Those familiar with the lightning arrester art will understand that a plurality of lightning arrester-s similar to lightning arrester 1 may be electrically connectd in series and the number of primary spark gaps within any given arrester may be varied as desired, depending upon the particular sparkover voltage level and reseal voltage level that a given system requires. The circuit components 28 through34 shown in FIG. 2 will be described below, with reference to FIG. 3.

In FIG. 3 of the drawing, there is shown a top plan view of the porous insulating disc B of spark gap assembly 15, which was depicted in FIG. 1. A pair of primary spark gap electrodes 23 and 24 are spaced apart a predetermined distance and mounted on the upper surface of disc B to define a primary spark gap therebetween. Any suitable conventional means may be utilized to retain the primary electrodes 23 and 24 in this spaced-apart relation on the disc B. The electrodes 23 and 24 respectively contain integral arc running horns 23' and 24' which form a horn gap that serves to rapidly move and stretch, or lengthen an are formed between the electrodes 23 and 24 outward therefrom in a manner well known in the art. The top surface of insulating disc B is substantially fiat, except for the raised integral teeth 25 positioned at equally spaced intervals around approximately one-half of its circumference and a ridge 41 around its periphery. It will be understood that the bottom surface of the insulating disc A of spark gap assembly 15 (see FIG. 1) is also generally flat, but is also provided with raised teeth that are adapted to fit in interlocking relation with the teeth 25 on the upper surface of plate B in a manner such that an arc-stretching passageway is defined by the respective interlocking teeth on the discs A and B when an arc is moved from the spark gap 23-24 into engagement with these teeth. Such tortuous arc lengthening passageways are well known in the lightning arrester field and it will be appreciated that my invention is not limited in this regard to the particular structure illustrated herein.

Electrode 23 is illustrated as being diagrammatically connected by a conductor 26 to a valve resistor 13 and then to ground by a second conductor 27. It will be appreciated that this diagrammatic illustration is merely a simplified schematic arrangement that is utilized for purposes of abbreviating the description of the invention. Of course, the more conventional circuit arrangement shown in FIG. 2, which includes the additional primary spark gap C-D in series with the nonlinear resistance 13 more accurately reflects the circuit utilized in the lightning arrester 1. Also, for purposes of simplifying the description, the electrode 24 is shown directly connected, by a conductor 21, to a conductive bus 22 of a system that is to be protected. It should be understood that the bus 22 is intended to normally conduct a direct current at a predetermined, substantially constant voltage level. In order to improve the operating characteristics of the spark gap assembly 15, pursuant to the teaching of my invention, a pair of auxiliary electrodes 28 and 29 are mounted at predetermined spaced points on the periphery of the upper surface of plate B. The electrode 28 is electrically connected by a suitable conductor 30 through a series resistor 31 to primary spark gap electrode 23. The other auxiliary electrode 29, is, in like manner, electrically connected by a suitable conductor 32 through a series resistor 33 to the other primary spark gap electrode 24 of the spark gap assembly 15. A capacitor '34 is electrically connected, as shown in FIG. 3, between the conductors 30 and 32 and, thus, between the auxiliary electrodes 28 and 29. In this preferred embodiment of my invention, the resistors 31 and 33 are selected to limit the current that will flow in the auxiliary electrode circuit when a surge voltage is impressed across the primary spark gap electrodes 23 and 24. Also, in this embodiment of the invention, the auxiliary electrodes 28 and 29 are positioned in preformed apertures through the upper surface of ridge 41 on disc B, and glued into position thereon in a manner such that an arc magnetically blown out from the primary spark gap electrodes 23 and 24 will electrically contact the inner tips of the auxiliary electrodes 28 and 29 simultaneously. The capacitance of capacitor 34 is selected so that it can store a suitably large electric charge to properly facilitate extinction of an arc in the arcing chamber of the spark gap assembly 15, as will be described below.

In the operation of this preferred embodiment of the spark gap assembly of my invention, it will be understood that the spacing between primary spark gap electrodes 23 and 2-4 is sufficient to prevent an are from forming between these electrodes when only normal line voltage is present on the protected system 22. When a high voltage surge is transmitted fi'om the system 22 by the conductor 21 to the spark gap electrode 24, the electrodes 23 and 24 sparkover if this voltage exceeds their predetermined sparkover voltage rating. Since valve resistor 13 presents a relatively low impedance to a high voltage surge, the surge is discharged through the arrester to ground without unduly endangering the insulation or operatin components of the system 22. After the high voltage su ge has been successfully discharged, D-C power-follow ,current will continue to flow through the arc 35 even after the combined action of the horn gap 23'-24-' and the elec tromagnetic field developed by the coil 19* serve to move the are 35 outward fromthe spark gap defined by the electrodes 23 and 24 into engagement with the arc-stretching teeth 25. However, in this lengthened position, the arc voltage is substantially increased and this voltage charges the capacitor 34, through resistor 33, to a voltage level that is dependent on the size of resistors 31 and 33' selected in a given application, but which is susbtantially equal to the arc voltage in the preferred embodiment of the invention. At this point in the reseal cycle of the spark gap operation, the auxiliary electrodes 28 and 29 come into contact with the lengthening arc 35. As soon as this electrical contact is established, it will be seen that a series circuit including the charge capacitor 34 is completed across the electrodes 28 and 29 by the are 35; accordingly, since the voltage charge on capacitor 34 is equal to the entire arc voltage, whereas the voltage drop across the are between the electrodes 28 and 29 is only equal to approximately one-third of the overall arc voltage, the capacitor .34 is instantaneously discharged into the arcing chamber and, thus, extinguishes the portion of the are 35 between the electrodes 28 and 29'. Specifically, it should be noted that the arrangement of the electrodes 28 and 29 with respect to the capacitor 34 causes the discharge current from the capacitor 34 to buck, or oppose, the polarity of the primary arcing current 35 between the auxiliary electrodes 28 and 29. By thus extinguishing at least onethird of the are 34, an extremely high dielectric; namely the air gap between auxiliary electrodes 28 and 29, is effectively introduced into the series circuit between spark gap electrodes 23 and 24, therefore, the are 35 is extinguished and does not restrike since only the normal line voltage of the system 22 is now impressed across the primary spark gap.

It will be seen that the electrode 28 is shown as extending into the arcing chamber 36 to a predetermined point adjacent the innermost ends of the teeth 25 such that it is positioned over a passageway 42 formed by an aperture in the top surface of the plate member B. The passageway 42 (see FIG. 4) afliords a gas conducting conduit between the primary arcing chamber 36 and an auxiliary arcing chamber 37 formed in the insulating disc, or plate member B beneath, and substantially parallel to the plane of the primary arcing chamber 36. It will be noted that in this embodiment of the invention, the innermost end of auxiliary electrode 28 lies in a vertical plane that is on the inner side of the center line of electromagnetic coil 19. In this arrangement, the above described operation of the magnetic field developed by electromagnetic coil 19, which drives arc 35 outward from spark gap electrodes 23 and 24, also functions to move the discharge are formed between auxiliary electrodes 28 and 29 in the opposite direction. In other words, this reverse electromagnetic force, coupled with the flow of arc-generated gases into the auxiliary arcing chamber 37, serves to drive the reverse current discharge are formed between the auxiliary electrodes 28 and 29 into the chamber 37 where it is rapidly lengthened and quenched. In addition, this secondary arcquenching feature of the invention is enhanced by a pair of arc-running conductive members 37' and 37" (see FIG. 3) which are mounted in arcing chamber 37 to form a horngap whose horns diverge outwardly away from the outer surface of disc B, generally toward the spark gap electrodes 23 and 24. To further facilitate this arc driving action, the auxiliary arcing chamber 37 is vented to the surrounding atmosphere through passageway 38. Of course, it should be understood that a tortuous arc-stretching surface may be provide adjacent the periphery of the auxiliary arcing chamber 37, if desired, and other gas venting means than the passageway 38 may be utilized without departing from the scope of my invention.

An important feature of my invention is its capability of providing a precise, readily preset arc quenching, or reseal voltage for the spark gap assembly 15. Referring to FIG. 5, there is shown another embodiment of the invention which, in addition to other unique features, illustrates a preferred means for providing these desirable operating characteristics. Specifically, between the insulating plate members A and B there is shown one of the auxiliary electrodes 28, which comprises a threaded metallic member that may be rotated to adjust the spacing of its innermost end with respect to the primary arc gap electrodes 23 and 24. In this embodiment of the invention, the auxiliary electrodes 28 and 29 are disposed within the arcing chamber 36 so that their innermost ends are adjacent the outer peripheral wall or ridge 41, of the spark gap assembly 15. Therefore, an arc 35 (see FIG. 2) stretched between the primary spark gap electrodes 23 and 24 must be moved outward from the primary spark gap to a point near its maximum extension before it electrically contacts the auxiliary electrodes 28 and 29, which introduce a reverse polarity electric discharge into the arc from a voltage source, such as capacitor 34 to facilitate extinction of the are 35, as described above. It will be apparent that since the primary arc voltage is directly proportional to the arc length and the degree of engagement between the arc and the tortuous path defined by the teeth 25, the voltage at which the auxiliary electrodes 28 and 29 come in contact with the arc 35 can be precisely adjusted by rotating the auxiliary electrodes 28 and 29 to adjust the spacing of their respective innermost ends with respect to the primary spark gap electrodes 23 and 24. In this manner, the arc quenching, or reseal voltage of the spark gap assembly can be accurately set within fairly wide limits.

In addition to demonstrating the adjustable voltage, are quenching feature of my invention, the embodiment of the invention shown in FIG. 5 depicts a gas venting passageway 39 having one of its ends disposed directly beneath the innermost end of the auxiliary electrodes 28 and 29 and its other end communicating with the outer surface of insulating plate member B. It will also be noted that the innermost ends of the auxiliary electrodes 28 and 29 are disposed directly over the center of electro-magnetic coil 19. Due to this relative positioning of the auxiliary electrodes, 28 and 29 with respect to coil 19, when an are 35 comes in contact with these electrodes, the are moving force applied to it by the magnetic field generated by coil 19 is substantially neutral, i.e., the magnetic field generated by coil 19 does not drive the discharge arc formed between the electrodes 28 and 29 either inward or outward with respect to the outer peripheral surfaces of plate members A and B. Accordmgly, the primary arc-moving force on an are formed between the auxiliary electrodes 28 and 29 is supplied by the venting of are generated gases through the exhaust passageway 39. These gases force the reverse current discharge arc formed by current from the capacitor 34 to move toward the outer periphery of the plate members A and B 'where it is again subjected to the electromagnetic field generated by the coil 19. The magnetic field adjacent the outer surface of members A and B drives the reverse current are outward, so these combined forces quickly lengthen the discharge arc and extinguish it to thus facilitate extinction of the primary arc 35 between the spark gap electrodes 23 and 24, as described above with reference to FIG. 3.

It will be apparent from the foregoing discussion that the arc extinguishing capability of my invention can be adjusted by varying the capacitance of capacitor 34 or the size of the resistors 31 and 33, as well as by changing the relative spacing of the auxiliary electrodes 28 and 29 so that a greater or lesser portion of the primary are 35 is subjected to a reverse polarity discharge current when it contacts these auxiliary electrodes. Various applications of the invention will determine the optimum relation between these particular settings and sizes and, of course, all such combinations fall within the scope of my invention.

Turning now to FIG. 6, still another embodiment of my invention is shown to further demonstrate the flexibility of its application. For purposes of simplifying the description of this embodiment of the invention, the schematically depicted components and circuit diagram elements may be regarded as similar in construction and function to those shown in FIG. 3 where like identifying numerals are utilized as reference numbers for them. Thus, an insulating plate member B having a primary arcing chamber 36, and arc-stretching teeth 25 on its upper surface is shown with respect to a D-C electric power system 22 and a valve resistor 13, which in turn are respectively connected by conductors 21, 26 and 37 to ground, in Series with primary spark gap electrodes 23 and 24. An auxiliary electrode 40, in the form of a threaded, rotatably mounted metallic screw, is electrically connected in shunt relation with the primary spark gap defined between primary electrodes 23 and 24 by con ductors 30 and 32 which complete a series circuit including a current limiting resistor 33 and a capacitor 34. It will be apparent that the primary difference between the embodiment of my invention depicted in FIG. 6 and the embodiment shown in FIG. 3 resides in the fact that only one auxiliary electrode, 40 is utilized in the FIG. 6 embodiment, whereas two auxiliary electrodes 28 and 29 were used in the FIG. 3 embodiment.

It will be understood that the operation of the embodiment of the invention shown in FIG. 6 differs somewhat from the operation of the invention described above with reference to FIG. 3. Specifically, when a transient overvoltage surge from system 22 causes an are 35 to be formed between the primary electrodes 23 and 24, the arc is rapidly moved outward from the primary spark gap into contact with the auxiliary electrode 40. During the interval of time required to move the are 35 across the arcing chamber 36, the capacitor 34 is charged through resistor 33 to a voltage substantially equal to the voltage drop across the arc 35. Consequently, at the instant that the arc 35 contacts the auxiliary electrode 40 the polarity of that portion of arc 35 between electrode 24 and the auxiliary electrode 40 is reversed as capacitor 34 discharges into the arcing chamber 36 and, thus, the extinction of this portion of arc 35 is facilitated.

Of course, the particular are voltage across the primary are 3-5 at which it contacts auxiliary electrode 40 can be adjusted, as described above with reference to FIG. 3, by rotating the threaded contact 40 to vary its spacing with respect to the primary spark gap electrodes 23 and 24. Since there is only a single auxiliary electrode 40 in this embodiment of my invention, it 'will be appreciated that a simplified and accurate means of ad- 8 justing the ratio of reseal to sparkover voltage for the lightning arrestor 1 has been provided.

It will also be understood that although a capacitor 34 has been shown and described herein as a source of arc-quenching discharge voltage, other suitable voltage sources may be substituted without departing from the teaching of my invention. Similarly, although the arcquenching feature of the invention has been described in conjunction with one primary spark gap of a lightning arrester, it will be apparent that this feature may be utilized with any portion of the primary current limiting gaps of a given arrester, as individual circumstances require.

While there has been shown and described various preferred embodiments of my invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein Without departing from the true spirit and scope of the invention, which is set forth with particularity in the following appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spark gap assembly comprising, in combination, means defining an arcing chamber having a spark gap therein, are moving means for moving an are formed in said gap outward therefrom, auxiliary electrode means disposed in spaced relation to said spark gap and adapted to electrically contact an are moved outward from said gap, a source of voltage, circuit means electrically connecting said auxiliary electrode means to said source of voltage, said auxiliary electrode means, said source of voltage and said circuit means being operative in response to an arc contacting said auxiliary electrode means to facilitate extinction of the arc.

2. A spark gap assembly as defined in claim 1 wherein said source of voltage comprises an electrical capacitance shunt connected across said spark gap, whereby said capacitance is electrically charged by a voltage developed across said spark gap.

3. A spark gap assembly as defined in claim 2 including current limiting means electrically connected in series with said capacitance and in shunt relation with said spark gap.

4. A spark gap assembly as defined in claim 1 wherein said auxiliary electrode means is spaced a predetermined distance from said spark gap.

5. A spark gap assembly as defined in claim 4 including means for readily varying said predetermined distance after said assembly is assembled.

6. A spark gap assembly as defined in claim 4 wherein said auxiliary electrode means comprises one electrode spaced in relation to said spark gap to contact an are moved outward from said spark gap at a point adjacent the mid-point of the are.

7. A spark gap assembly as defined in claim 1 wherein said auxiliary electrode means comprises a plurality of spaced-apart electrodes.

8. A spark gap assembly as defined in claim 7 wherein said source of voltage is electrically connected by said circuit means to develop a voltage between at least two of said plurality of spaced-apart electrodes.

9. A spark gap assembly as defined in claim 8 wherein said circuit means are arranged such that the voltage developed between at least two of said plurality of spacedapart electrodes has a polarity opposed to the polarity of the primary arc voltage across said spark gap.

10. A spark gap assembly as defined in claim 7 including means defining an auxiliary arcing chamber, said auxiliary arcing chamber being adapted to receive an are formed between at least two of said plurality of spacedapart electrodes.

11. A spark gap assembly as defined in claim 10 including electro-magnetic are moving means adapted to move an are formed in said spark gap outward therefrom toward the outer surface of said spark gap assembly, said plurality of spaced-apart electrodes being disposed adjacent the outer surface of said spark gap assembly where the arc moving capability of said electromagnetic means is relatively weak.

12. A spark gap assembly as defined in claim 11 wherein said spark gap and said plurality of spaced-apart electrodes are disposed in relation to the spark gap assembly so that a common plane intersects a predetermined portion of each of them, and said electromagnetic means comprises an electrically conductive coil disposed in a plane substantially parallel to said common plane.

13. In a lightning arrester, a valve resistance means electrically connected in series with at least one spark gap assembly comprising means defining a primary arcing chamber, a pair of main electrodes disposed in spacedapart relation to define a spark gap therebetween within said primary arcing chamber, arc moving means for moving an are formed in said spark gap outward therefrom, a pair of auxiliary electrodes disposed in spaced-apart relation within said primary arcing chamber and adapted to electrically contact an are moved outward from said I spark gap, a source of voltage, circuit means electrically connecting said source of voltage to said pair of auxiliary electrodes to develop a voltage therebetween, said developed voltage being effective to facilitate extinction of an are moved outward from said spark gap when the arc contacts said pair of auxiliary electrodes.

14. In a lightning arrester as defined in claim 13 wherein said arc moving means includes means defining a first arc-moving horn gap adjacent said spark gap, and further includes means defining a second arc-moving horn gap adjacent said pair of auxiliary electrodes, means defining an auxiliary arcing chamber, said first horn gap being disposed in said primary arcing chamber and said second horn gap being disposed in said auxiliary arcing chamber.

15. The invention defined in claim 14 wherein said first horn gap diverges toward the outer surface of said spark gap assembly, and said second horn gap diverges away from the outer surface of said spark gap assembly.

16. The invention as defined in claim 15 wherein said second horn gap diverges in a direction generally toward the center of said spark gap assembly.

17. The invention as defined in claim 14 including means defining a passageway between said primary arcing chamber and said auxiliary arcing chamber, said passage- Way being adapted to conduct arc-generated gases between said chambers, the movement of such gases being adapted to accelerate movement of an electric arc formed between said pair of auxiliary contacts toward the diverging arc-running surfaces of said second horn gap.

18. The invention as defined in claim 15 wherein said auxilary arcing chamber comprises essentially a gas venting passageway adapted to discharge arc-generated gases from said primary arcing chamber to the exterior of said assembly.

References Cited UNITED STATES PATENTS 1,194,195 8/1916 Jackson 317-61.5 X 2,565,945 8/1951 Bockman 31777 X 2,789,253 4/1957 Vang 3171l X 3,159,765 12/1964 Schultz 317-74 X 3,354,345 11/1967 Stetson 31774 X J D MILLER, Primary Examiner H. FENDELMAN, Assistant Examiner US. Cl. X.R. 317-70, 74, 78 

